And also overseas, another chess move in the duel with north korea overnight, the u.S. Flexing its muscle and sending stealth bombers into the backyard of the mysterious nation. The north korean news agency says they're burning with hatred over this latest move and martha raddatz has the story. Reporter: If north korea had any doubt that the u.S. Would defend its ally south korea, this rare show of force should end it. The two, massive b-2's soared 6,500 miles from missouri to drop dummy weapons on a bombing range west of south korea and less than 50 miles from the north korean border. And then flew back to the u.S. It was the first time the u.S. Military has confirmed a b-2 practice mission, but the message was clear. The b-2 is capable of dropping 16 nuclear bombs, each on a different target. It can fly under any weather conditions, penetrating sophisticated air defenses with its radar evading stealth skin. Ngets we will unequivocally defend and we are unequivocally committed to that alliance with south korea. And we will be prepared, if we have to be prepared, to deal with any eventuality there. Reporter: Since february when the u.S. And south korea began gearing up for military exercises, north korea steadily escalated its threat, a page from its playbook, only this time those threats have been hotter, including nuclear strikes, which they are not yet capable of. The u.S. Says the stealth bombers were not meant to ratchet up the tension with north korea, but that is exactly what has happened.

This transcript has been automatically generated and may not be 100% accurate.

U.S. Deploys Stealth Bombers Amid Tension in Korea

The military shows that it is taking new threats from Kim Jong Un seriously.

North Korea Mobilizes for War, Threatens U.S.

North Korea says it has moved rockets in preparation for a strike against United States.

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